This application relates generally to the field of cranial burr hole covers, and more particularly relates to such covers structured in the nature of clamps wherein a member positioned interiorly on the skull and a member positioned exteriorly on the skull are locked together to cover the burr hole.
In cranial surgery it is often necessary to cut burr holes through the skull to directly access a portion of the brain or to provide an access means for the insertion of saws or other cutting implements in order to remove a larger section of the skull, often referred to as a flap. In order to secure the flap to the skull once the flap is replaced, it is known to provide craniotomy pins, such as shown in U.S. Pat. No. 5,549,620 to Bremer. The pins comprise a large external head possessing lateral dimensions greater than the width of the gap between the flap and skull, a post or shaft member sized to be able to reside within the gap, and an internal locking member. The internal locking member is generally rectangular in shape and is sized to have a longitudinal dimension greater than the width of the gap and a lateral dimension smaller than the width of the gap. With this configuration, the longitudinal dimension of the internal locking member of the craniotomy pin is aligned with the gap such that the internal locking member can be pushed into the gap. The pin is then rotated so that the longitudinal dimension is now perpendicular to the gap, the ends of the internal locking member precluding removal of the pin without rotation of the pin. The craniotomy pin of this configuration is not designed for use in covering the burr holes disposed at the ends or midportion of the gaps, since the longitudinal dimension of the internal locking member would need to greater than the diameter of the burr hole, which is several times greater than the width of the gap. This would make rotation of the pin difficult and possibly cause damage to the underlying tissue. The craniotomy pin of this configuration is not suitable in any way for covering isolated burr holes where no flap has been removed and replaced, since there is no gap for insertion and then rotation of the internal locking member. Furthermore, the fixed separation distance between the external head and the internal locking member does not allow adjustment of the clamping pressure, i.e., movement of the external head toward the internal locking member.
It is known to provide clamping covers, i.e., adjustable covers that can be tightened onto the skull or bone flap, for the both gaps and burr holes, wherein the covers comprise a disk-shaped internal member and a disk-shaped external member held together by a connecting member provided with a locking mechanism, such as a ratchet system or screw threading. For use with burr holes, the diameter of the internal and external disk-shaped members must be greater than the diameter of the burr hole. This structure is suitable for use in circumstances where a flap portion of the skull has been removed between burr holes, since the internal disk-shaped members can be laterally positioned on the interior side of the skull prior to replacement of the skull. However, such covers cannot be utilized to cover an isolated burr hole, since the required size for the internal disk-shaped member prevents it from being inserted directly through the burr hole. An example of such a clamping cover is sold under the brand CRANIAL LOOP by KLS Martin Group.
Other cranial burr hole covers suitably structured to cover an isolated burr hole are shown in U.S. Pat. No. 6,126,663 to Hair and in U.S. Pat. No. 8,241,342 to Kirschman. The Hair device utilizes a plurality of leg-like connecting members extending from the external cover, with each connecting member terminating in an outwardly extending foot-like structure. In the neutral position the leg-like connecting members bend inward and can be inserted into the burr hole. A threaded spreading post is then driven into an axial opening to drive the foot-like structures radially outward to be positioned on the inside of the skull. This device is not depth-adjustable, as the distance between the foot-like members and the external cover is fixed. The structure of the device also requires excessive time to place each burr hole cover.
The Kirschman device comprises a pair of generally parallel connecting members extending through a disk-shaped cover member. Each connecting member has an outwardly extending tab member. The connecting members are flexed together to reduce the radial extension of the tab members for insertion through the burr hole. Once inserted the proper distance, the tab members are pressed outward to position them on the inside of the skull. The connecting members are provided with a ratchet surface that cooperates with slots in the external cover, such that the cover member can be pressed downward onto the skull to secure the device to the skull and cover the isolated burr hole. The portions of the connecting members extending above the external cover are then removed. Because the tab members are structured to flex inwardly, proper placement of the device requires the surgeon to maintain the spread of the tabs after insertion using an instrument or a finger while simultaneously lowering the external cover into the clamped and secured position.
It is an object of this invention to provide an adjustable cranial burr hole cover suitable for use with single, isolated burr holes, and a method of covering an isolated burr hole using this cover, wherein the problems inherent known burr hole covers are overcome.